Microtubules are members of an array of fibrous cytoskeleton proteins which control cell strength and molecular movement within the cell. In particular, microtubules are critical to chromosomal movement during cell division. Microtubules are comprised of tubulin subunits which form a diverse array of both permanent and transient structures. The processes of microtubule assembly and disassembly are dynamic and can be affected by various factors including temperature, anti-cancer drugs such as colchicine and taxol, and microtubule-associated proteins (MAPs). MAPs are involved in the formation and the stabilization of microtubules.
One major family of MAPs, assembly MAPs, can be identified in neurons as well as non-neuronal cells. They are responsible for cross-linking microtubules in the cytosol. These MAPs are organized into two domains: a basic microtubule-binding domain and an acidic projection domain. The projection domain is the binding site for membranes, intermediate filaments, or other microtubules. Based on sequence analysis, assembly MAPs can be further grouped into two types: Type I MAPs include MAP1A and MAP1B; and Type II MAPs include MAP2a, MAP2b, MAP2c, MAP4, and Tau.
Type I MAPs are large, filamentous molecules that co-purify with microtubules and are abundantly expressed in brain and testis. They contain several repeats of the amino acid sequence KKEX. This positively charged motif binds and neutralizes negatively charged tubulin, thus stabilizing tubulin by eliminating the repulsion between tubulin subunits. MAP1A and MAP1B are composed of a heavy chain and multiple light chains. Two of the light chains, light chain 1 (LC1) and light chain 2 (LC2), are derived from the 3' end of the open reading frames that encode the MAP1A and MAP1B heavy chains.
A third light chain, LC3, has recently been characterized in rat and mouse (Mann, S. S. et al (1994) J. Biol. Chem. 269:11492-11497). LC3 is a 16.4 kDa molecule that binds MAP1A, MAP1B, and microtubules. It is suggested that LC3 is synthesized from a source other than the MAP1A or MAP1B transcripts, and the expression of LC3 may be important in regulating the microtubule binding activity of MAP1A and MAP1B during cell proliferation.
The discovery of proteins related to a human microtubule-associated protein and the oligonucleotides encoding them satisfies a need in the art by providing new compositions which are useful in diagnosing, preventing, and treating disorders associated with cell proliferation.